Gaseous electrical discharge lamp



EVLEMMERS 2,329,124

Sept. 7, 1943.

' GASEOUS ELECTRICAL- DISCHARGE LAMP Filed Dec. 30, 1940 Eu ene Lemmefs,

His Aklnrneg.

Patented Sept. 7, 1943 cAsEoUs ELECTRICAL mscmmcr. LAMP Eugene Lemmers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application December 30, 1940, Serial No. 372,213

11 Claims.

My invention relates to gaseous electric discharge lamps and more particularly to a high pressure metal vapor lamphaving an extended illuminating surface of high intrinsic brilliance.

In the past, gaseous discharge lamps have not been readily adaptable to certain fields of application, such as motion picture projection for ex ample, because such fields generally require a source in which a large amount of light energy is cbncentrated within a small crosses'ectional area if the optical systems of the apparatus involved are to produce clear images. Low pressure gaseous discharge lamps fail in this requirement because their light output perv unit'area of luminous surface is relatively small, 1. e., they have low intrinsic brilliance. In recent years high pressure lamps of extremely high intrinsic brilliance, such' as the so-called mercury vapor capillary lamps, have been developed. These, however, have not been entirely satisfactory for the reason that the high pressure tends to constrict the arc to a very fine thread and although the arc may have high intrinsic brilliance, it is,

- ne ertheless, undesirable as alight sovrce because of its geometrical configuration.

Now, I have found that the above disadvantage in high pressure lamps can be overcome by providing a lamp of the aforesaid high pressure type with a flattened arc chamber and by operating it under the conditions of pressure and current density hereinafter specified. When's'o operated the arc is not only made to spread out into a stable and highly brilliant source of substantial area but it is also caused to emit many new spectral lines which improve the general spectral quality of the lamp.

It is accordingly an object of my invention to provide an improved high pressuregaseous discharge lamp of high intrinsic brilliance and having a luminous surface of substantial area.

It is another object of my invention to provide an improved light source for projection and like purposes. 7 a

A still further object of the invention is to provide a lamp of improved spectral quality.

Further objects and advantages on the invention will become apparent from the following detailed description and the accompanying draw,- ing in which Fig. '1 shows a view, partly in section, of a lamp constructed in accordance with the invention along with a-circuit for operating the same, while Fig. 2 shows across-section taken along the line 2-2 of Fig. 1. v

Referring to Fig. l, the lamp i comprises an envelope 2, preferably of glass or quartz, in which sure may be limited to any desired value.

are sealed the electrodes 3 3 which-may be of the type generally used in capillary lamps. For example, they may consistv of a central core of thorium within a spiral coil f tungsten wire or they may be formed by a tungsten coil activated by a suitable material such as barium or strontium carbonate. They may even be of the liquid type formed by pools of mercury, for example,

if means are provided for cooling them to a sufilciently low temperature to maintain the low vapor pressure required. If solid electrcdes are used, a small amount of mercury or other suitable material provides asource of metal vapor and is inserted in the envelope 2 in the usual manner during the evacuation process. In addition, a small amount of an ignition gas may be added, for example 1 0 mm. of argon. As indicated by the cross-sectional view of Fig. 2, the envelope 2 is of flattened shape. The cross-section at the inner surfaces of the envelope may, for example, have dimensions of the order of x .060". Energy for operation of the lamp may be provided by the secondary winding 8 of the leakage reactance transformer 9 which i energized by any suitable source of alternating current power l0 through the primary winding II. The transformer provides the necessary ballast for the lamp.

In order that the pressure may be kept at the desired low value, it will generally be necessary that the vapor atmosphere be unsaturated during the operation, i. e., that insufiicient mercury or other metal be present to furnish the amount of vapor which the envelope would normally hold in a vaporized state at the temperature .of operation. Thismay be accomplished by limiting the quantity of material introduced into the envelope to such an extent that it is completely vaporized before the device attains its operating temperature. In this manner the normal operating pres- Of course, if an excess of mercury is used, the pressure may still be kept low by artificial cooling but ing to enlarge it and vice versa. Thus, with high pressures such as obtain in the conventional type of high pressure capillary lamp, the arc will conof atmospheres.

centrate in a narrow thread 4 which follows ap- .y the shortest distance between the however, the current strength is iliCiBElScd the arc will be forced to expand in order that it may obey its natural tendency to follow the path of least electrical resistance provided, or" course, that the pressure is prevented pillary lamp.

Generally speaking, the current necessary to flatten the arc will be roughly proportional to the pressure or to some low power thereof. I am unable at this time to state an exact relationship between the two factors. .With very high'pressures the current density necessary to flatten the arc becomes prohibitive for all practical purposes because with envelope materials presently available, the heat developed tends to melt the envelope. I would estimate the practical upper pressure limit for presently available materials to be not greater than about atmospheres. It thus becomes necessary to reduce the pressure in order to flatten the are at a current within the range of practicality. On the other hand, if too low pressures are resorted to, the light output per unit area is disadvantageously decreased since, as is wellknown, the light output from a gaseous discharge varies with pressure. I have found, for example, that at pressures below about one-half of one atmosphere, the light intensity or intrinsic brilliance is too low to be useful for such fields of application as motion picture projection. The upper limit of pressures is dependent largely on the materials available for cathode and envelope fabrication, i. e., the envelope must be made of a material which can withstand heating effect of the high current density necessary to flatten the arc. With the materials now available, the upper limit of pressure is of the order It will be understood, of course, that when new materials capable of withstanding the heat are found, lamps capable of employing the principles of the invention at pressures above the limits specified above may be constructed. In any event, it is thus necessary to strike a compromise between the limiting conditlons of pressure and current if 'a current of practical value is to be used and a useful amount of light obtained.

I have constructed lamps with flattened chambers within pressure ranges of 0.5 to 5 atmospheres. a x 0.060" cross-section, 60 amperes or more were needed to flatten the discharge into the flat chamber. Thus, at 2 atmospheres, at least approximately 2700 amperes per square inch or 4 amperes per square millimeter are needed to flll the envelope of this size. For lamps with crosssections of 0.005" x in the pressure range 0.5 to 5 atmospheres, the flattening would occur above 3 amperes or a current density of about 1600 amperes per square inch or 2.4 amperes per square milln. eter.

It will be understood that any suitable cooling means as a liquid bath or air blast may be used to aid in maintaining the low pressure. I have found the liquid bath most effective.

It will further be understood that the lamp herein disclosed is but one form of my invention and that many modifications within the scope of the appended claims may occur to those skilled in the art to which the invention appertains. For example, many different tube configurations may be employed. Further, other metallic vapors may be used, although in general the specified current densities and pressures will be changed somewhat if the same results are to be obtained. All suchmodifications I aim to include within the scope of the appended claims.

What I. claim as new and desire to secure by Letters Patent of the United States is:

1. A gaseous electrical discharge lamp of the high pressure type comprising, an envelope having a flattened transverse cross-section, a pair of electrodes disposed within said envelope and capable of supporting a discharge therein longitudinally of the envelope-a quantity of vaporizable material 'in said envelope suflicient in amount to produce an operating vapor pressure of at least about 0.5 atmosphere, means for sup plying sufiicient-electrical energy to establish said operating pressureand for supplying suificient current between said electrodes to produce a discharge of sufficient density to cause the discharge to substantially fill said cross-section.

2. A gaseous electrical discharge lamp of the high pressure type comprising, an envelope having a flattened transverse cross-section, a pair of electrodes disposed within said envelope and capable of supporting a discharge therein longitudinally'of the envelope, a quantity of vaporizable material in said envelope 7 suflicient in amount to produce an operating vapor pressure of at least about 0.5 atmosphere, means for sup- With a pressure of 2 atmospheres and plying suflicient electrical energy to establish said operating pressure and for supplying suflicient.

current between said electrodesto produce a discharge of suflicient density to cause the discharge to substantially fill said cross-section, said quantity of vaporizable material being insufficient to produce a. saturated vapor atmosphere in said envelope at the normal operating temperature.

3. A gaseous electrical discharge lamp of the about 0.5 atmosphere, means for supplying sufficient electrical energy 'to establish said operating pressure'and for supplying sufficient current between said electrodes to produce a discharge of sufilcient density to cause the discharge to substantially fill said cross-section and cooling means for aiding the maintenance of the operating vapor pressure within practical limits, said quantity of vaporizable material being insufficient to produce a saturated vapor atmosphere in said envelope at 1 the normal operating temperature.

4. A gaseous electrical discharge lamp of the high pressure type comprising, an envelope having a flattened transverse cross-section, a pair of,

atmosphere, means for supplying sufli cient elecnally .of the envelope, a quantity of mercury in said envelope sufficient in amount to produce an millimeter and cooling means for aiding the operating vapor pressure of at least about 0.5

atmosphere, means for supplying sufllcient electrical energy to establish said operating pressure and for supplying sufficient current between said electrodes toproduce adischarge of a density of at least about 2.4 amperes per square millimeter, and cooling means for aiding the maintenance of the operating vapor pressure within practical limits, said quantity of mercury being insufficient to produce a saturated vapor atmosphere in'said envelope at the normal operating temperature.

6. A gaseous electrical dischargelamp of the high pressure type comprising, an envelope having a flattened transverse cross-section, a pair of electrodes disposed within said envelopev and capable of supportinga discharge therein longitudinally of the envelope, a quantity of mercury in said envelope sufficient inamount to produce an operating vapor pressure of the order of 0.5'

to 5 atmospheres, means for supplying suflicient electrical energy to establish said operating pressure and for supplying suflicient current'between said electrodes to produce a discharge of a density of at least about 2.4 amperes per square I millimeter, said quantity of vapor being insuflito 5 atmospheres, means for supplying sufficient electrical energy to establish said operating pres-- sure and for supplying sufilcient current between said electrodes to produce a discharge of a density of at least about 2.4 amperes per square maintenance of the operating vapor pressure within said pressure range, said quantity of vapor being insufiicient to saturate said lamp at its normal operating temperature.

8. The method of operating a gaseous electric discharge lamp of thetype having a flattened transverse cross-section between electrodes and a high vapor pressure, which comprises the steps of maintaining the pressure at a fixed value.

above about 0.5 atmosphere and passing sufiicient current therethrough to cause the discharge to substantially fillsaid elongated crosssection. f v

9. The method of operating a gaseous electric discharge lamp of the type having a flattened transverse cross-section between electrodes and a high vapor pressure, which comprises the steps of maintaining the pressure within a range of the order of 0.5 to 5 atmospheres and passing suflicientcurrent therethrough to cause the discharge to substantially fill said' elongated crosssection.

10. The method of operating a gaseous electric dischargelamp of the type having a flattened transverse cross-section between electrodes and a high vapor pressure, which comprises the steps of maintaining the vapor in an unsaturated state at operating. temperature and maintaining the pressure within a range of the order of 0.5 to 5 atmospheres and passing sufiicient current there- "through to cause thedischarge to substantially fill said elongated cross-section.

cient to saturate said lam'p" at its normal operating temperature.

7. A gaseous electrical discharge lamp of the high pressure type comprising, an envelope having a flattened transverse cross-section, a pair of electrodes disposed within said envelope and capable of supporting a discharge therein longitudinally of the envelope, a quantity of mercury in saidenvelope suflicient in amount'to produce an operating vapor pressure of the order of 0.5

11. The method of operating a mercury vapor electric discharge lamp of the type having a flattened-transverse cross-section between elec-' trodes and a high vapor pressure, which comprises'the steps of cooling said lamp to aid in maintaining the pressure within a range of the order of 0.5 to 5 atmospheres and passing a current of density of at least 2.4 amperes per square millimeter therethrough to cause the discharge to substantially fill said elongated cross section.

EUGENE Lemmas. 

